1. Field of the Invention
The present invention pertains to encapsulated substances. More particularly, the present invention pertains to microcapsules, encapsulating materials and methods applicable to the preparation of microcapsules, encapsulated microgranules, encapsulated microdroplets and the like, as well as to methods of use thereof.
2. Prior Art
Conventional encapsulation methods available up to the present time can generally be classified as either physical.mechanical encapsulation methods or chemical encapsulation methods. Included among conventional chemical encapsulation methods are physicochemical methods such as coacervation, interfacial polymerization methods, in situ methods and the like.
In the case of physical.cndot.mechanical encapsulation methods, particle size control is generally achieved through control of the physical conditions under which the involved processes are carried out. With chemical encapsulation methods, particle size control can be achieved through addition of hydrophilic substances such as emulsifiers (surfactants), protective colloids, etc., and through adjusting the amount and/or type of such hydrophilic substances. In addition, particle size control with chemical encapsulation methods can be effected through adjustment of various chemical and physical conditions such as mixing speed, pH, temperature, reaction rate, etc. during one or more of the steps involved in the chemical encapsulation method.
In the case of the invention disclosed in Japanese Patent Application, First Publication Serial No. Sho-51-129485 wherein unsaturated polyester resin modified with hydrophilic polyethylene oxide is employed as a part of a wall forming component, even though an emulsifier (surfactant) and/or water soluble resin are utilized therewith, pigment containing microcapsules having a relatively large average diameter of on the order of 2 to 25 .mu.m are produced. With the invention disclosed in Japanese Patent Application,. Second Publication Serial No. Sho-58-501631, the liquid crystal microcapsules prepared according thereto using polyvinyl alcohol and/or gelatin as water soluble resin again have a comparatively large diameter, ranging from 2 to 25 .mu.m. In the method disclosed in Japanese Patent Application, First Publication Serial No. Sho-62-254483 as well, the pigment containing microcapsules formed thereby using emulsifier (surfactant) and water soluble protective colloid resin have a diameter on the order of 5 .mu.m.
In the method disclosed in Japanese Patent Application, First Publication Serial No. Sho-57-190647, water insoluble resin is utilized as one wall forming component, and secondary processing using surface activating agents and the like is carried out. Although encapsulation is carried out in an aqueous solution of water soluble protective colloid resin such as gelatin or gum arabic which functions as a small particle stabilizing agent, the diameter of the resulting microcapsules ranges from 2 to 25 .mu.m.
With all of the various methods thus described, the diameter of the smallest microcapsules which can be produced is on the order of several micrometers. In particular, those produced by physical.cndot.mechanical encapsulation methods tend to have a relatively great diameter. With chemical encapsulation methods by which means comparatively smaller microcapsules can be produced, by increasing the amount of hydrophilic constituents whereby wall forming material and core forming material are dispersed, even smaller diameter microcapsules can be produced, although even so, diameters of less than 1 .mu.m can be achieved only with great difficulty. Even with various attempts which have been made using unacceptably large amounts of auxiliary agents such as hydrophilic substances, the goal of achieving sub-micron order sized microcapsules has been unattainable as yet. As described previously, up to the present time, it has similarly not been possible to produce microcapsules having diameters of 1 .mu.m and less using emulsifying agents, hydrophilic protective colloids, and various other types of auxiliary agents.
As a particular example of an application of microcapsules, paints, inks and similar products can be prepared using encapsulated pigments. However, in order to produce a product which provides a highly attractive, super high-gloss surface, so-called ultramicrocapsules having a diameter of 1 .mu.m and less are required. Furthermore, from the standpoint of producing a durable, long lasting super high-gloss surface, generally minimal use of hydrophilic substances therein is desirable.
In view of the preceding discussion, it can be appreciated that encapsulation technology in its present state is inadequate when applied to super high-gloss paints. That is to say, means are not presently available for the production of sufficiently small diameter ultramicrocapsules which can be used in paints and the like so as to provide for super high-gloss finishes through the use thereof. Furthermore, with the incorporation of various hydrophilic substances which is generally employed at present as the means to produce microcapsules having a size approaching that of ultramicrocapsules, a corresponding deterioration in the durability and endurance characteristics of finished surfaces resulting from the use thereof occurs.